1. Field of the Invention
This invention relates to a method of suppressing gear-shifting shock in an automatic transmission vehicle, and more particularly to a method of suppressing gear-shifting shock in an automatic-transmission vehicle by changing the engine output power in response to the gear-shifting operation of the automatic transmission.
2. Description of the Prior Art
When an automatic transmission shifts from one gear speed to another gear speed, the engine speed changes due to a change in the gear ratio, while the vehicle speed hardly changes because of the inertia of the vehicle body, which causes fluctuations in the torque transmitted through the automatic transmission. When the torque transmitted through the automatic transmission fluctuates, the acceleration of the vehicle body fluctuates and a so-called gear-shifting shock is produced.
As is well known, the gear-shifting shock can be suppressed, for instance, by temporarily changing the engine output power during the gear-shifting.
Changes in the engine output power must be timed with the initiation and completion of the gear-shifting. For example, if the engine output power is kept low after the gears have shifted while the vehicle is accelerating, the performance of the vehicle during acceleration will deteriorate. On the other hand, if the reduction of the engine output power is terminated and the engine output power is increased while the gears are still in the process of shifting, the load on the friction coupling elements in the automatic transmission will increase and the durability of the elements will suffer.
Since the engine speed changes based on a certain characteristic curve in response to the initiation and completion of the gear-shifting, the initiation and completion of the gear-shifting can be detected through the change in the engine speed as disclosed in Japanese Unexamined Patent Publication No. 55-69738, for instance.
Generally, the curve representing the changes in the engine speed or the turbine speed during gear-shifting has points of inflection where gear-shifting is initiated or completed. Accordingly, by detecting the points of inflection, the initiation and the completion of the gear-shifting can be detected. However, the points of inflection cannot be sufficiently clear, depending upon what the operating condition of the engine is during the gear-shifting. This problem may be overcome by setting a gear-shifting completion speed range (on the basis of which the completion of the gear-shifting is determined) by multiplying the speed at the time when the gear-shifting command is generated by the gear ratio of the gear speed into which the automatic transmission is going to shift.
However, the speed at which the friction coupling elements in the automatic transmission finish engaging varies depending on the difference between the friction coupling elements, changes in the friction coupling elements which have occurred over time, the viscosity of the oil in the automatic transmission, the torque transmitted from the engine and the like. For instance, the smaller the torque transmitted from the engine, the earlier the friction coupling elements finish engaging. That is, the speed at which the gear-shifting is completed fluctuates according to various factors. Accordingly, if the gear-shifting completion speed range is always set in the same way, the gear-shifting completion speed range will not always be set correctly, and the gear-shifting shock will not always be sufficiently suppressed.